Israel's Jewish Agency came to the rescue of two Jewish Ukranian families after rebels seized control of Donetsk airport as they were waiting to emigrate to Israel, an agency spokesman said on Tuesday.

Jewish immigration from Ukraine has more than doubled since the start of the year over 2013 figures, the agency said. Israel has seen 762 immigrants arrive from Ukraine between January and April, compared to 315 over the same period a year ago.

The agency is preparing to help facilitate the departure of more families from Donetsk should the hostilities there continue.

Agency chairman Natan Sharansky, a former Soviet dissident who was born in Donetsk, said in a statement: "Due to the current situation in the country we have significantly expanded our activities, assisting those who wish to immigrate to Israel."

An estimated 11,000 Jews live in Donetsk and about 130,000 in all of Ukraine.

An Israeli immigration official said some recent newcomers from Ukraine to Israel had flown in initially as tourists then asked for citizenship. Israeli law offers citizenship to any Jews who apply for it.

Sharansky himself was jailed for his human rights activities in the then Soviet Union and was freed in 1986 after nine years in prison as part of an East-West spy swap.